The sails on my new boat
Are 'low mile' sails,(in extremely good condition) but were stored for over 8 years folded up, full of creases that act permanant. So I'd say loosely rolled with no tight creases would be the best way to store them. Though I think the easiest way to avoiod creasing them would be to take them out then re-pack them every now and then. I'd remove any lines or hardware, battens etc before storage, place them in a small canvas (old denim pant legs make great little storage bags with a little sewing work)
I'll second the plastic tote idea, should keep the critters out and allow loose storage all at the same time. Mine were also stored on the shelf in the garage where some kind of oil got on them, so I had large yellowish blotches on them, smelled and tasted organic, so I assumed it was a vegetable base (suntan lotion or cooking oil maybe) and tried dishwashing soap and purple power which removed nearly all of the stains. I'd say if mine had been in totes, I wouldn't have needed to clean them. Plus it's just a lot easier to store a couple totes, stack them in the closet, corner of the garage etc. four or 5 totes stacked is a neat stack, four or 5 bags stacked is just a pile.
Ken.